Method of manufacturing magnetically anisotropic permanent magnets with a crystal orientation



O Umted States Patent n113,545,525

[72] Inventor Albertus Antonie Aldenkamp [51] Int. C1. H011 l/04, Emmasingel, Eindhoven, Netherlands H01f 7/02 [21] Appl. No. 676,642 [50] Field ofSearch 164/82, [22] Filed Oct. 19,, 1967 122,128,146; 148/101, 31.57 [45] Patented Dec. 8, 1970 [73] Assignee U.S. Philips Corporation [56] References cued New York, N.Y. UNITED STATES PATENTS I cbrmrafion of Delaware by meme 2,398,018 4/1946 Linley et a1 164/146X 1551811111611 3,189,957 6/1965 Luteijn 164/82 1 1 Priority (kt-211N966 3,314,828 4/1967 Harrison 148/3 1 .57 [33] Netherlands l 3 l 1 No. 6614748 Prunary Examrner-J. Spencer Overholser Assistant Exammer-John E. Roethel W Anorney- Fank R. Trifari [54] METHOD OF MANUFACTURING ABSTRACT: An Fe-Co-Ni-Al al 1oy suitnble for continuous 2 chum, No Drawings casting of crystel oriented magnetically anlsotroplc permenent magnets contalnmg not more than 0.15 percent of slhcon U-S- Cl. is continuously cast in a tube and cooled at such a rate as to prevent the formation of a 'y-phase.

'ANISOTROPIC PERMANENT MAGNETS WITH A CRYSTAL ORIENTATION The invention relates to a method of manufacturing crystal oriented magnetically anisotropic permanent magnets consisting of a Fe-Co-Ni-Al alloy containing; in addition to Fe and the usual impurities, approximately 15 to 42 percent of Co, approximately 10 to 20 percent of Ni, approximately 6 to 10 percent of Al, up to 8 percent of Cu and any additions such as, for example, Si, up to 4 percent of Nb, up to 8 percent of Ta, while the content of Nb and/or Ta-may be replaced entirely or in part by Ti. The invention also relates to an alloy suitable for the1manufacture of crystal oriented magnetically anisotropic permanent magnets.

Such methods are known from Dutch Pat. Specification l09,8ll and the Dutch application 289,045 laid open for public inspection. These methods have the great advantage that permanent magnets which have satisfactory magnetic. properties (for example, H, 750 Oe; Br 13500 G; (Bl-1),, 8 X 10 G. e) can be manufactured in a comparatively simple manner by a continuous process. This involves great economic advantages; Moreover, the magnets thus manufactured have a constant quality within small tolerances.

- It has been found that with the use of the aforesaid casting methods, the continuous casting process was sometimes interrupted because the solidified alloy clogged in the tube. A tube in which the alloy has once clogged must be replaced. This involves large expenditures for materialand mounting.

It has been found that pure Al; 0;, sintered to compactness is a' particularly suitable material for the tube, inter alia because it has the following properties: it does not dissolve in the alloy, it has a high melting point, a low porosity and a high resistance to wear. p t t Investigations have shown that clogging of the rod inthe A1 0;, tube may be due to reactionsof the solidifying alloy with the wall of the tube.

It is common practice in the manufacture of permanent magnets consisting ofa Fe-Co-Ni-A] alloy to provide a quantity of Si lying between approximately 0.15 and 5 percent phase isrequired. So it seemed that the use of an alloy poor in by means of the continuous casting process either by choosing the rate of drawing above agiven minimum value, or by cooling the tube sufficiently.

According to the invention, the alloy which 18 supplied in the molten state at the upper end of an A1 0 tube and is withdrawn in the solid state at the lower end of this tube conpreferably a quantity lying between 0.2 and 0.4 percent in this I alloy. Such an addition prevents the formation of a cubic-face centered 'y-phase besides'the already available cubic-spacecentered a-phase during cooling of the alloy after solidification. The presence of this 'y-phase detrimentally affects the permanent magnetic properties of the material. If no Si were added, the said 'y-phase would actually be formed during cooling and the material would have to be subjected to an additional-and hence cost-increasing--thermal treatment in order to eliminate said 'y-phase.

investigations have shown [that the aforesaid reactions between the wall of the tube and the alloy are due to the fact that the M 0 of this tube wall is more readily attacked with higher silicon content of the alloy. During these experiments, it had been ensured that the alloy was'poor in oxides, since these oxides also react with the wall of the tube so that clogging of the rod could also be due to these oxides. Therefore, attempts had to be made to prevent contact between the tains at the most 0.15 percent of Si, while the cooling rate is at least 0.4 C./sec'.

Experiments have shown that with an alloy containing 0.5 percent of Si, the casting process stagnated after 3 hours, with a content of 0.35 percent of Si after 24 hours and with an Sicontent of 0.15 percent after one week. It has been found that no further improvement can be obtained by further reducing the Si-content. A further reduction of the Si-content below 0.]5 percent no longer has any influence on the reaction between the alloy and the wall .of the tube, which is due to the fact that in this case, other effects, which are dominated at a higher Si-content by the Si-effect, start playing a part. When the temperature gradient in the tube is chosen to be suffi' ciently large, i.e.,-so that for a given rate of drawing, the corresponding rate of coolingofthe solidified alloy is, for example, A? C./sec. or 1 C./sec., it has been found that the formation of a 'y-phase is prevented.

For example, an alloy consisting of 28 percent by weight of Co, 14 percent by weight of nickel, 8 percent by weight of aluminum, 3 percent by weight of copper, 2 percent by weight of titanium, 0.1 percent by weight of silicon and the balance iron was introduced in molten form into an A1 0 tube having an inner diameter of 18.5 mm. under an argon atmosphere. A bar was drawn form the other end of the tube in which the direction of the crystals were oriented axially at the rate of 7 mm./sec. The temperature gradient within the tube was about l5C./min. and the cooling-rate 2C./sec. V

- While the invention has been described in connection with a particular example, other modifications will be apparent to those skilled in the art without departing from the spirit and ly 15 to 42 percent of Co, approximately 10 to 20 percent of v Ni, approximately 6 to 10 percent of Al, up to 8 percent of cu, up to 4 percent of Nb and up to 8 percent of Ta, up to 8 percent of Ti and the balance iron and impurities in which the alloy is supplied in the molten state at the upper end of an A1 0 tube and is withdrawn in the solid state at the lower end of the tube, the improvement comprising supplying alloys containing at the most 0.15 percent of Si, and cooling the alloy in the tube at a rate of at least O.4C,/:sec. to prevent the formation of a 'y-phase in the alloy.

2, A method of manufacturing crystal oriented magnetically anisotropic permanent magnets as claimed in claim 1 in which 

